That's true to a degree, b/c each Chapter controls everything that directly supports them, sometimes even to the manufactorums that provide equipment and ammo. However, as a percentage, very few of the total personnel in all that are Space Marines.
And then there's the Space Wolves...who decided to use the Codex to start the fires in the stills they use to manufacture Mjod. Mjod, the only substance that can actually get a Space Marine drunk.
Luv me some Wolves!